Dating K&E Slide Rules
Dating a particular K&E slide rule can be a challenge. In most cases dating of a particular slide rule requires consideration of several parameters. Model numbers, serial numbers, catalog descriptions, cursor types, patent dates, variants, and specials are used in combination with each other to fully identify a given rule. The following is a discussion on the subject.
Model Numbers: There were four
different number series in the history of the slide rule line.
Serial numbers started in 1924 beginning with 0 and going through 999999 then rolling over to 0 again. There were three rollovers occurring in 1943-1944, 1954, and 1962. In general the production rate was about 70,000 rules per year until the 1950s. In the 1950s and it was over 100,000 per year. The 1960s had a production rate of about 100,000 per year for several years and tapering off in the 1970s ending at about 700000. In general it is safe to assume a linear production rate between the rollover dates particularly for the common types rules.
Serial numbers can be used to approximate the manufacture date of a given rule however not necessarily the sales date. The common rules were produced in regular batches but the specialty rules did not sell as well and a given batch of rules might stretch over several years. It is not uncommon to find rules in the 1960s in 68 xxxx series packaging but 4000 series model numbers on the rules. The Fuller and Thacher's slide rules had their own serial number systems.
On early rules the serial numbers were usually on the rule in two places, the end of the slide and the bottom edge of the frame. The presence of two serial numbers on a given rule was to facilitate manufacturing allowing the mating of pieces of rules in final assembly. The slides and frame were cut from the same piece of stock and for best stability over the life of the rule they should be mated together in final assembly. From the 1950s on the serial number is on the slide and the last three digits of the number is repeated on the frame pieces to facilitate this mating.
Prior to 1924, mating of the rule parts was through the use of numbers stamped into the end of the rules on both the frame and the slide. These numbers were probably used for each batch of production and do not seem to have any other significance.
Full line K&E catalogs were produced every five to six years except in the early 1900s where it was about every three years. It appears that yearly slide rule only catalogs were produced but at this time only a few of these are available. There were also Educational Products catalogs that contained slide rules.
Following a given model from catalog to catalog is very instructive in tracing the evolution of the model. A date range for a given model can be established doing this. Many of the major variations of a given model can be observed and thereby putting a date range on that variant.
Care must be taken in assuming that a particular model was carried between any two full line catalogs. There are cases of entire models coming and going between full line catalog issues. There are slide rule model numbers that never appeared in any catalogs.
There are mistakes in the catalogs both in descriptions and illustrations. Many of these are subtle and usually do not make much difference.
In the 1930s and 1940s some of the illustrations show serial numbers on the rules. Some people think these numbers have significance. If they do it probably is limited to being that it might have been a real serial number at the time the illustration was drawn. Many of these illustrations were used over and over in many catalogs and obviously the serial numbers did change in that time frame.
The cursors used on K&E slide rules evolved over the years. When they changed, all production of all models was switched over. There is a definite timeline to the cursor models.
- Before 1906 ------ Slide rules either had no cursor, a brass chisel type cursor, or a metal framed glass cursor.
- 1913 - 1915 ------- A complex cursor that has been named the "column cursor" was introduced for duplex rules.
- 1915 --------------- All slide rules were fitted with an all glass cursor. The first issue had metal end blocks.
- 1916 - 1933 ------- The metal cursor cursor blocks on the all glass cursor were replaced with plastic ones.
- 1933 - 1935 ------- The plastic cursor blocks were modified to have flanges to cover the edge of the glass.
- 1936 - mid 1950s - The "improved cursor" with a metal rim around the glass was introduced.
- mid 1950s - 1975 - The glass cursor lenses are replaced with molded plastic ones.
The presence of a given cursor on on a rule can sometimes be misleading. Replacement cursors were sold for all previous models.
Patent and copyright dates are often quoted by sellers of slide rules implying that the rule is that old. The date of a patent only means that the rule was not produced before that date.
It is very common to see 4053-3s for sale quoting the 1900 patent date. The first production of the 4053-3 was in 1913. The 1900 patent date shows up on all 4053-3s until the beginning 1930s. The 1900 patent was for generic construction techniques used on all Mannheim type rules.
Copyright dates in instruction manuals suffer from the same problem as patent dates. Very often it is necessary to do a page for page comparison of two manuals with different copyright dates to find out if there is a difference. Manuals before 1920 are poorly organized and often contain instructions for several types of rules.
K&E slide rules evolved continually. On a given rule you will find that scale sets, model numbers, construction methods, printing styles, packaging, and logos evolved. A particular family of rules such as the 4088 gained members and lost some over its life span. Some of the variants are visible in catalogs, others are not. Knowing the existence of these variants can help in identifying a particular rule. Understanding this subject has been the drive behind this website. For the avid K&E collector these variants are a nightmare and a blessing at the same time. The collecting will never end. The puzzle will never be completed. There is always another rule to look for.
Example: 4053 Family of slide rules
The 4053 first appeared in the 1909 catalog as just a 10" rule with no dash number. The dash number scheme for designating length was introduced in 1913. The 4053 and 4088 families were the first use of the dash number scheme. A 5" plastic version of the 4053 is listed in the 1972 catalog. The following is a brief history of the 4053 family of slide rules as is told in the K&E catalogs that are available at this time. Exact timing is not possible because of the time between catalogs.
- 1909 -- The 10" 4053 was introduced without a dash number.
- 1913 -- The full family was introduced with dash numbers and the F version.
- 1915 -- The "frameless" all glass cursor was introduced with metal cursor blocks.
- 1916 -- The metal cursor blocks of the all glass cursor were replaced with plastic ones.
- 1922 -- The K scale was moved from the bottom edge to the front of the rule and a centi-meter scale was placed on the bottom edge.
- 1925 -- All of the 4053 model number designations were changed. The N prefix was added: N4053-2, N4053-3, N4053-3F, and N4053-5.
- 1933 -- The plastic cursor blocks had flanges added to them to protect the ends of the glass.
- 1936 -- The improved metal framed cursor was introduced.
- 1939 -- Only the N4053-3, N4053-3F, N4053-5 appears in the catalog.
- 1942 -- Only the N4053-3 and N4053-5 are shown in the catalog.
- 1954 -- The model number of the N4053-3 was changed to 4053-3, the profile shape of the body was changed, and the conversion tables on the rear were printed directly without a paper label. The N4053-5 remained unchanged.
- 1959 -- The 4153-1 and 4153-C 5" plastic slide rules were first mentioned in the 1959 Price Sheet. 1960 -- A special brochure for pocket slide rules shows the 4153-1 and 4153-1C.
- 1962 -- The 4053 numbers were converted to the 68 series of numbers. The 20", 10", and 5" are described.
- 1972 -- Only the 5" Pocket rule was listed with a group of Pocket Slide Rules.
Each of the major family groups of slide rules have equivalent stories. The 4080/4081 families have a very fascinating series of variants.
Unfortunately much of the information on these variants is known only by collectors that have studied them extensively. This web site is an attempt to desiminate this information.
K&E produced many special purpose slide rules. Some became catalog items and some were commissioned specials. The ones that became catalog items can be tracked using the catalogs. The commissioned specials are abundant and go back to the early 1900s and extend to the end of slide rule production in 1975.